Modern coating applications of the interiors of objects relies upon spray gun technology. A typical spray gun that has a barrel, has a nozzle at the lower end and a feed mechanism at the upper end, often a body which is part of a recirculating loop of paint, lacquer or other coating.
Traditionally, the cans/containers descend in a track into a rotating star wheel, which is oriented vertically. As the star wheel rotates, the cans/containers pass in front of the spray gun, which has been adjusted for the size and shape of cans/containers being sprayed, and the spray gun is activated by automated controls for a brief period of time (some milliseconds) during which it coats the interior of the can/containers. The process continues during a production run (or during several shifts or several days) and coats the interior of hundreds/thousands of cans/containers per minute. Various means and methods might be employed to speed up the act of spraying the can/containers during a run, however, the present invention is not directed at that. This invention is instead to the industrial process of adjusting the spray guns between production runs.
In most instances, adjusting spray guns requires an iterative process, partially science and partially trial-and-error, due to the broad array of can shapes and sizes and the wide range of possible adjustments therefrom.
In most prior art, a spray gun is mounted so that it can be adjusted in three dimensions. The three degrees of freedom are vertical and horizontal linear changes (two degrees of translation) and a rotation of the spray gun about the mount (one degree of rotation). The problem may be seen in exaggerated and simplified form in PRIOR ART FIG. 5.
PRIOR ART FIG. 5 shows a spray gun and mount and a range of motion in rotation. It may be seen that when the spray gun in the first position 501 may be rotated by a sweep angle * and becomes the spray gun in the second position 501′, it rotates about a focal point H. Point H is determined, of course, for engineering convenience in designing the gun mount. (Note that the gun 501 is simplified and the sweep angle * is vastly exaggerated for clarity.)
Examining PRIOR ART FIG. 5 it may be seen that the gun nozzle is in a different physical location. Thus, while the gun nozzle has been adjusted in angular measure (rotated) it has now moved (translated) to a new location.
However, the traditional vertical star wheel does not compensate for this motion: the pocket holding the cans to be sprayed will still be located and oriented in the same place as always.
This means that the operators must now adjust the gun a second time, this time in two dimensions of translation, in an attempt to properly locate the gun nozzle. However, the spray pattern made by the gun may change when it is moved, requiring a repetition of the original step of adjusting the angle. This may then require another adjustment in location and so on.
In practice, the location may be likely to be adjusted first, setting off the same cycle. This process can take a considerable amount of time, depending upon the individual adjusting the nozzle.
Since the can/container may be possibly to be used for food or beverage products, such as aluminum or steel beverage cans, regulations or the spray gun manufacturer may require some form of certification/documentation of the actual positioning of the gun after each adjustment, prior to beginning a production run.
It would be preferable to provide a spray gun mount which avoids these problems, difficulties and inefficiencies of adjustment between production runs.